Air conditioner

ABSTRACT

A refrigerant circuit ( 15 ) is disposed which is formed by connection of an outdoor unit ( 11 ) and two indoor units ( 12, 13 ). And, the air conditioning capacity of the outdoor unit ( 11 ) is controlled such that the temperature of refrigerant circulating through the refrigerant circuit ( 15 ) becomes a target value and the target value is altered correspondingly to the state of an operation. In other words, the control characteristics of the target value are determined correspondingly to the air conditioning load characteristics of a building, and the target value is altered according to the control characteristics and based on the inside/outside temperature difference between an indoor set temperature and an outside air temperature. For example, during cooling mode operations, the control characteristics of an evaporating temperature target value are determined correspondingly to the cooling load characteristics of the building and thereafter the evaporating temperature target value is altered according to the control characteristics and based on the inside/outside temperature difference. And, the air conditioning capacity of the outdoor unit ( 11 ) is controlled such that an evaporating temperature that a low-pressure pressure sensor ( 74 ) detects becomes a target value.

TECHNICAL FIELD

[0001] The present invention relates to air conditioning systems. Moreparticularly, this invention relates to measures to control airconditioning capacity.

BACKGROUND ART

[0002] A conventional multi type air conditioning system in which aplurality of indoor units are connected to a single outdoor unit, suchas one disclosed in Japanese Patent Kokai Publication No. H02-230063,has been known.

[0003] The indoor unit comprises a first compressor which invertercontrols capacity and a second compressor which controls capacity bymeans of an unload mechanism. And the outdoor unit adjusts the capacityof air conditioning by controlling the capacity of each of the twocompressors.

[0004] In other words, during cooling mode operations, the capacity ofeach of the two compressors is controlled such that evaporatingtemperature becomes a given value, whereas, during heating modeoperations, the capacity of each of the two compressors is controlledsuch that condensing temperature becomes a given value.

[0005] On the other hand, the indoor unit adjusts the capacity ofcooling by performing control so that the degree of superheating becomesconstant, for example during cooling mode operations.

[0006] Problems that the Invention Intends to Solve

[0007] In the above-described conventional air conditioning system, theair conditioning capacity of the outdoor unit is controlled such thatevaporating temperature or condensing temperature maintains a constantvalue all the time. In other words, in conventional air conditioningsystems, the air conditioning capacity of an outdoor unit is controlledso as to maintain a plurality of indoor units in such a state that eachindoor unit is able to continuously exhibit a respective specified airconditioning capacity.

[0008] In the foregoing air conditioning system, the evaporatingtemperature or the condensing temperature is held at a fixed value. Thismeans that, even when it is sufficient for an indoor unit to operate ata less air conditioning capacity, the outdoor unit is operated at agreat air conditioning capacity.

[0009] Therefore, even when the air conditioning load is small duringfor example an intermediate period, the indoor unit operates at the sameair conditioning capacity as when the air conditioning load is at itsmaximum, thereby resulting in an excess of capacity.

[0010] As a result of the above, the frequency at which the indoor unitis repeatedly operated and stopped becomes higher. This producesproblems, that is, room temperature varies greatly and the capacity ofcompressors becomes unstable.

[0011] Further, the frequency at which the compressor is repeatedlydriven and stopped becomes higher, which causes the drop in durabilitydue to stress produced when the compressor is driven or stopped.

[0012] Furthermore, the excess of air conditioning capacity producesproblems such as a poor operating efficiency and an uneconomicaloperation.

[0013] Bearing in mind the above-mentioned problems, the presentinvention was made. Accordingly, an object of the present invention isto suppress air conditioning capacity excess and to reduce both thefrequency at which a utilization unit is repeatedly operated and shutdown and the frequency at which a compressor is repeatedly driven andshut down.

DISCLOSURE OF THE INVENTION

[0014] The present invention is an invention for variably controllingthe control target value of a heat source unit.

[0015] More specifically, the first invention is directed to an airconditioning system for providing air conditioning, the air conditioningsystem comprising a refrigerant circuit (15) formed by connection of aheat source unit (11) and a plurality of utilization units (12, 13, . .. ). In this invention, the air conditioning capacity of the heat sourceunit (11) is controlled such that a physical quantity of refrigerantcirculating through the refrigerant circuit (15) becomes a target value,and wherein the target value is altered and set.

[0016] Further, the second invention is directed to an air conditioningsystem for providing air conditioning, the air conditioning systemcomprising a refrigerant circuit (15) formed by connection of a heatsource unit (11) and a plurality of utilization units (12, 13, . . . ).The second invention further comprises a capacity controlling means (91)for controlling the air conditioning capacity of the heat source unit(11) so that a physical quantity of refrigerant becomes a target value,and a target value adjusting means (92) for altering the target value ofthe capacity controlling means (91).

[0017] Further, the third invention is an invention according to thesecond invention in which the target value adjusting means (92) isconfigured so as to variably control the target value correspondingly tothe air conditioning load characteristics of a building.

[0018] Further, the fourth invention is an invention according to thesecond invention in which the target value adjusting means (92) isconfigured so as to variably control, according to the controlcharacteristics of the target value and based on the temperaturedifference between a set temperature of an air conditioning space and anoutside temperature, the target value.

[0019] Further, the fifth invention is an invention according to thesecond invention in which the target value adjusting means (92) includesa deciding means (93) for determining the control characteristics of thetarget value correspondingly to the air conditioning load characteristica building, and an altering means (94) for variably controlling,according to the target value control characteristics determined by thedeciding means (93) and based on the temperature difference between aset temperature of an air conditioning space and an outside temperature,the target value.

[0020] Further, the sixth invention is an invention according to any oneof the first to fifth inventions in which during cooling mode operationsthe refrigerant physical quantity is an evaporating pressure.

[0021] Further, the seventh invention is an invention according to anyone of the first to fifth inventions in which during cooling modeoperations the refrigerant physical quantity is an evaporatingtemperature.

[0022] Further, the eighth invention is an invention according to anyone of the first to fifth inventions in which during heating modeoperations the refrigerant physical quantity is a condensing pressure.

[0023] Further, the ninth invention is an invention according to any oneof the first to fifth inventions in which during heating mode operationsthe refrigerant physical quantity is a condensing temperature.

[0024] Further, the tenth invention is an invention according to any oneof the first to fifth inventions in which the air conditioning capacityof the heat source unit (11) is controlled by controlling the capacityof each compressor (41, 42) of the heat source unit (11).

[0025] Further, the eleventh invention is an invention according toeither the third invention or the fifth invention in which the buildingload characteristics are determined based on the amount of internal heatgeneration of the building and the amount of external heat.

[0026] Further, the twelfth invention is an invention according to thefifth invention in which a temperature detecting means (74) for thedetection of refrigerant evaporating temperatures during cooling modeoperations is provided. And, the capacity controlling means (91), whichtakes as a refrigerant evaporating temperature a target value duringcooling mode operations, is configured to control the air conditioningcapacity of the heat source unit (11) so that an evaporating temperaturethat the temperature detecting means (74) detects becomes the targetvalue. In addition, the deciding means (93) of the target valueadjusting means (92) is configured so as to determine the controlcharacteristics of the target value of the evaporating temperature.Furthermore, the altering means (94) of the target value adjusting means(92) is configured so as to variably control the target value of theevaporating temperature.

[0027] Further, the thirteenth invention is an invention according tothe fifth invention in which a temperature detecting means (76) for thedetection of refrigerant condensing temperatures during heating modeoperations is provided. And, the capacity controlling means (91), whichtakes as a refrigerant condensing temperature a target value duringheating mode operations, is configured to control the air conditioningcapacity of the heat source unit (11) so that a condensing temperaturethat the temperature detecting means (76) detects becomes the targetvalue. In addition, the deciding means (93) of the target valueadjusting means (92) is configured so as to determine the controlcharacteristics of the target value of the condensing temperature.Furthermore, the altering means (94) of the target value adjusting means(92) is configured so as to variably control the target value of thecondensing temperature.

[0028] Further, the fourteenth invention is an invention according toany one of the fourth, fifth, twelfth, and thirteenth inventions inwhich the target value adjusting means (92) is configured such that thetarget value control characteristics are set manually.

[0029] Further, the fifteenth invention is an invention according to anyone of the fourth, fifth, twelfth, and thirteenth inventions in whichthe target value adjusting means (92) is configured such that the targetvalue control characteristics are set based on an input signal fed fromexternal setting means (9 b) via a communication line (9 a).

[0030] Further, the sixteenth invention is an invention according to anyone of the fourth, fifth, twelfth, and thirteenth inventions in whichthe target value adjusting means (92) is configured such the targetvalue control characteristics are automatically set by learningaccording to the state of an operation during air conditioning.

[0031] Finally, the seventeenth invention is an invention according tothe sixteenth invention in which the deciding means (93) of the targetvalue adjusting means (92) is configured such that the target valuecontrol characteristics are set by learning according to the number oftimes air conditioning operation is brought to a halt.

[0032] To sum up, in accordance with the present invention, refrigerantcirculates between the heat source unit (11) and the utilization units(12, 13, . . . ) for providing air conditioning. And, during airconditioning operations, the air conditioning capacity of the heatsource unit (11) is controlled such that a physical quantity ofrefrigerant in the refrigerant circuit (15) becomes a target value andthe target value is altered and set.

[0033] More specifically, for example, during cooling mode operations,the target value adjusting means (92) determines the controlcharacteristics of an evaporating temperature target value, and theevaporating temperature target value or evaporating pressure targetvalue is altered.

[0034] Further, during heating mode operations, the target valueadjusting means (92) determines the control characteristics of acondensing temperature target value, and the condensing temperaturetarget value or condensing pressure target value is altered.

[0035] When such a target value is altered, the capacity controllingmeans (91) takes a refrigerant evaporating temperature or a refrigerantcondensing temperature as a target value and controls the airconditioning capacity of the heat source unit (11) in such a way thateither an evaporating temperature that the temperature detecting means(74) detects or a condensing temperature that the temperature detectingmeans (76) detects becomes a target value. For example, compressorcapacity is controlled such that the evaporating temperature or thecondensing temperature becomes a target value.

[0036] Further, in the deciding means (93) of the target value adjustingmeans (92), either a target value control characteristic is manuallyset, a target value control characteristic is set based on an inputsignal fed from the external setting means (9 b) via the communicationline (9 a), or a target value control characteristic is automaticallyset by learning according to the state of an operation during airconditioning.

[0037] Effects of the Invention

[0038] Therefore, in accordance with the present invention, it isarranged such that a refrigerant temperature target value is alteredbased on an air conditioning load of a building for controlling the airconditioning capacity of the heat source unit (11), thereby making itpossible to perform operations at a corresponding air conditioningcapacity to the building air conditioning load.

[0039] That is, when it is sufficient for the utilization units (12, 13,. . . ) to operate at a less air conditioning capacity, the heat sourceunit (11) also can be operated at a less air conditioning capacity.

[0040] As a result, the utilization units (12, 13, . . . ) can beprevented from being operated at an excessive capacity during forexample an intermediate period. Because of this, it is possible toreduce the frequency at which the utilization units (12, 13, . . . ) arerepeatedly operated and shut down. And, in addition to making itpossible to reduce variation in the temperature of an air conditioningspace, compressor capacity can be made stable.

[0041] Further, since the frequency at which the compressors (41, 42)are repeatedly driven and shut down is reduced, this reduces stresswhich is produced when they are driven or shut down, thereby improvingthe durability of the compressors (41, 42).

[0042] Furthermore, since it is possible to suppress an excess of airconditioning capacity, this improves operating efficiency. As a result,COP (Coefficient Of Performance) is improved and improvements in economycan be achieved.

[0043] Further, in accordance with either the fourth invention or thefifth invention, the target value is altered depending on thetemperature difference between a set temperature and an outsidetemperature, whereby air conditioning capacity can be increased forexample at the beginning of an operation. For example, if the indoortemperature is higher than a set temperature during cooling modeoperations, or if the indoor temperature is lower than a set temperatureduring heating mode operations, this increases the temperaturedifference between either refrigerant evaporating temperature orrefrigerant condensing temperature and indoor suction air temperature,thereby making it possible to provide an increased air conditioningcapacity. As a result, it is possible to provide improved comfortability

[0044] Further, when there occurs sudden variation in load, the airconditioning capacity can be increased by making a change in the settemperature. This makes it possible to improve comfortability.

[0045] Furthermore, when performing air conditioning by introducingoutdoor air, the air conditioning capacity will vary depending on theinside/outside temperature difference, thereby further improvingcomfortability. For example, an air conditioning capacity required tomeet a set blow-out temperature is determined by the temperaturedifference between suction air temperature and set blow-out airtemperature. Because of this, it is possible for the heat source unit(11) to control a required minimum capacity, thereby making it possibleto improve COP and extend the range of controllable operations.

[0046] Further, if it is arranged such that the target value controlcharacteristic described above can be manually set, an air conditioningcapacity to meet the comfortability of a resident can be exhibited. Thiscertainly improves comfortability.

[0047] Furthermore, if it is arranged such that the target value controlcharacteristic described above can be learned, then a corresponding airconditioning capacity to the air conditioning load of a building can beset automatically. This provides further improvements in economy andcomfortability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048]FIG. 1 is a refrigerant circuit showing an embodiment of thepresent invention.

[0049]FIG. 2 is a characteristic diagram showing the loadcharacteristics of cooling of a building.

[0050]FIG. 3 is a characteristic diagram showing the controlcharacteristics of a target value of an evaporating temperature duringcooling mode operations.

[0051]FIG. 4 is a characteristic diagram showing the loadcharacteristics of heating of a building.

[0052]FIG. 5 is a characteristic diagram showing the controlcharacteristics of a target value of a condensing temperature duringheating mode operations.

[0053]FIG. 6 is a characteristic diagram showing a load characteristicversus control characteristic relationship during cooling modeoperations.

[0054]FIG. 7 is a characteristic diagram showing a load characteristicversus control characteristic relationship during heating modeoperations.

[0055]FIG. 8 is a control characteristic diagram showing the learning ofthe control characteristics of a target value during cooling modeoperations.

[0056]FIG. 9 is a control flow chart showing the controlling of capacityduring cooling mode operations.

BEST MODE FOR CARRYING OUT THE INVENTION

[0057] Hereinafter, an embodiment of the present invention will bedescribed in detail with reference to the accompanying drawings.

[0058] As seen in FIG. 1, an air conditioning system (10) of the presentembodiment comprises a single outdoor unit (11) and two indoor units(12, 13), in other words the air conditioning system (10) has aso-called multi type construction. The air conditioning system (10) isconfigured such that its operation is switchable between a cooling modeand a heating mode, and includes a refrigerant circuit (15) and acontroller (90).

[0059] The present embodiment employs the two indoor units (12, 13),which should be deemed as one example. Accordingly, in the airconditioning system (10) of the present invention, the numbers of theindoor units (12, 13) may be determined depending on the capacity andthe application of the outdoor unit (11).

[0060] The refrigerant circuit (15) is made up of a single outdoorcircuit (20), two indoor circuits (60, 65), a liquid side connectingpipe (16), and a gas side connecting pipe (17). The two indoor circuits(60, 65) are connected in parallel to the outdoor circuit (20) throughthe liquid side connecting pipe (16) and through the gas side connectingpipe (17), respectively. The liquid side connecting pipe (16) and thegas side connecting pipe (17) constitute connecting piping.

[0061] The outdoor circuit (20) is housed in the outdoor unit (11) whichis an outdoor machine. The outdoor unit (11) constitutes a heat sourceunit whereas the outdoor circuit (20) constitutes a heat source sidecircuit. The outdoor circuit (20) includes a compressor unit (40), afour-way selector valve (21), an outdoor heat exchanger (22), an outdoorexpansion valve (24), a receiver (23), a liquid side shutoff valve (25),and a gas side shutoff valve (26).

[0062] The compressor unit (40) is formed by connecting a firstcompressor (41) and a second compressor (42) in a parallel arrangement.Each compressor (41, 42) is formed by placing a compression mechanismand an electric motor for driving the compression mechanism in acylindrical housing. Neither the compression mechanism nor the electricmotor is shown.

[0063] The first compressor (41) is a compressor of a fixed capacitytype in which an electric motor is driven continuously at a fixed numberof revolutions. On the other hand, the second compressor (42) is acompressor of a variable capacity type in which the number ofrevolutions of an electric motor is changed step by step orcontinuously. And, the compressor unit (40) is configured such that thecapacity of the entire unit can be made variable by the driving andshutdown of the first compressor (41) and by making changes in thecapacity of the second compressor (42).

[0064] Connected to the compressor unit (40) are a suction pipe (43) anda discharge pipe (44). One end of the suction pipe (43) is connected toa first port of the four-way selector valve (21), whereas the other endthereof diverges into two branches which are connected to suction sidesof the compressors (41, 42), respectively. One end of the discharge pipe(44) diverges into two branches which are connected to discharge sidesof the compressors (41, 42), respectively, whereas the other end thereofis connected to a second port of the four-way selector valve (21). Oneof the branch pipes of the discharge pipe (44) that is connected to thefirst compressor (41) is provided with a discharge side check valve(45). This discharge side check valve (45) allows only flow of arefrigerant flowing out from the first compressor (41).

[0065] Further, the compressor unit (40) includes an oil separator (51),an oil return pipe (52), and an oil amount averaging pipe (54). The oilseparator (51) is disposed midway along the discharge pipe (44). The oilseparator (51) serves to separate refrigerating machine oil fromrefrigerant discharged from the compressors (41, 42). One end of the oilreturn pipe (52) is connected to the oil separator (51), whereas theother end thereof is connected to the suction pipe (43). The oil returnpipe (52) serves to return refrigerating machine oil separated in theoil separator (51) to the suction sides of the compressors (41, 42) andincludes an oil return solenoid valve (53). One end of the oil amountaveraging pipe (54) is connected to the first compressor (41), whereasthe other end thereof is connected to a portion of the suction pipe (43)in the vicinity of the suction side of the second compressor (42). Theoil amount averaging pipe (54) serves to average the amounts ofrefrigerating machine oil stored in the housings of the compressors (41,42) and includes an oil amount averaging solenoid valve (55).

[0066] A third port of the four-way selector valve (21) is pipingconnected to the gas side shutoff valve (26). A fourth port of thefour-way selector valve (21) is piping connected to an upper end of theoutdoor heat exchanger (22). The four-way selector valve (21) isswitchable between a state in which the first port and the third portcommunicate with each other while the second port and the fourth portcommunicate with each other (indicated by a solid line in FIG. 1) and astate in which the first port and the fourth port communicate with eachother while the second port and the third port communicate with eachother (indicated by a broken line in FIG. 1). By virtue of the switchingoperation of the four-way selector valve (21), the direction in whichrefrigerant in the refrigerant circuit (15) circulates is reversed.

[0067] The receiver (23) is a reservoir shaped like a cylinder andstores therein refrigerant. The receiver (23) is connected, through aninflow pipe (30) and an outflow pipe (33), to the outdoor heat exchanger(22) and the liquid side shutoff valve (25).

[0068] One end of the inflow pipe (30) diverges into two branch pipes(30 a, 30 b), whereas the other end thereof is connected to an upper endof the receiver (23). The first branch pipe (30 a) of the inflow pipe(30) is connected to a lower end of the outdoor heat exchanger (22). Thefirst branch pipe (30 a) is provided with a first inflow check valve(31). The first inflow check valve (31) allows flow of refrigerant onlyfrom the outdoor heat exchanger (22) toward the receiver (23). Thesecond branch pipe (30 b) of the inflow pipe (30) is connected to theliquid side shutoff valve (25). The second branch pipe (30 b) isprovided with a second inflow check valve (32). The second inflow checkvalve (32) allows flow of refrigerant only from the liquid side shutoffvalve (25) toward the receiver (23).

[0069] One end of the outflow pipe (33) is connected to a lower end ofthe receiver (23), whereas the other end thereof diverges into twobranch pipes (33 a, 33 b). The first branch pipe (33 a) of the outflowpipe (33) is connected to a lower end of the outdoor heat exchanger(22). The first branch pipe (33 a) is provided with the outdoorexpansion valve (24). The outdoor expansion valve (24) constitutes aheat source side expansion mechanism. The second branch pipe (33 b) ofthe outflow pipe (33) is connected to the liquid side shutoff valve(25). The second branch pipe (33 b) is provided with an outflow checkvalve (34). The outflow check valve (34) allows flow of refrigerant onlyfrom the receiver (23) toward the liquid side shutoff valve (25).

[0070] The outdoor heat exchanger (22) constitutes a heat source sideheat exchanger. The outdoor heat exchanger (22) is implemented by a finand tube type heat exchanger of a cross fin system. In the outdoor heatexchanger (22), heat exchange takes place between refrigerantcirculating through the refrigerant circuit (15) and outdoor air.

[0071] Further, the outdoor circuit (20) is provided with a gas ventpipe (35) and a pressure equalizing pipe (37).

[0072] One end of the gas vent pipe (35) is connected to the upper endof the receiver (23), whereas the other end thereof is connected to thesuction pipe (43). The gas vent pipe (35) constitutes a communicationpassage for introducing gas refrigerant in the receiver (23) to thesuction sides of the compressors (41, 42). Further, the gas vent pipe(35) is provided with a gas vent solenoid valve (36). The gas ventsolenoid valve (36) constitutes an opening/closing mechanism forconnecting and disconnecting flow of gas refrigerant in the gas ventpipe (35).

[0073] One end of the pressure equalizing pipe (37) is connected to thegas vent pipe (35) between the gas vent solenoid valve (36) and thereceiver (23), whereas the other end thereof is connected to thedischarge pipe (44). Further, the pressure equalizing pipe (37) isprovided with a check valve (38) for pressure equalization operable toallow flow of refrigerant only from one end thereof toward the otherend. If there occurs an abnormal increase in outside temperature whenthe air conditioning system (10) is out of operation, this may cause thepressure of the receiver (23) to become excessively high. In such acase, the pressure equalizing pipe (37) prevents, by relief of gasrefrigerant, the receiver (23) from bursting. During the operation ofthe air conditioning system (10), no refrigerant flows through thepressure equalizing pipe (37).

[0074] The indoor circuits (60, 65) are provided in the indoor units(12, 13), respectively. More specifically, the first indoor circuit (60)is housed in the first indoor unit (12) and the second indoor circuit(65) is housed in the second indoor unit (13).

[0075] Each of the indoor units (12, 13) constitutes a utilization unitand each of the indoor circuits (60, 65) constitutes a utilization sidecircuit.

[0076] The first indoor circuit (60) is formed by series-connecting thefirst indoor heat exchanger (61) and the first indoor expansion valve(62). The first indoor expansion valve (62) is piping connected to alower end of the first indoor heat exchanger (61), constituting autilization side expansion mechanism. The second indoor circuit (65) isformed by series-connecting the second indoor heat exchanger (66) andthe second indoor expansion valve (67). The second indoor expansionvalve (67) is piping connected to a lower end of the second indoor heatexchanger (66), constituting a utilization side expansion mechanism.

[0077] The first indoor heat exchanger (61) and the second indoor heatexchanger (66) each constitute a utilization side heat exchanger. Eachindoor heat exchanger (61, 66) is implemented by a fin and tube typeheat exchanger of a cross fin system. In each indoor heat exchanger (61,66), heat exchange takes place between refrigerant in the refrigerantcircuit (15) and indoor air.

[0078] One end of the liquid side connecting pipe (16) is connected tothe liquid side shutoff valve (25). The other end of the liquid sideconnecting pipe (16) diverges into two branches one of which isconnected to an end of the first indoor circuit (60) on the side of thefirst indoor expansion valve (62) and the other of which is connected toan end of the second indoor circuit (65) on the side of the secondindoor expansion valve (67). One end of the gas side connecting pipe(17) is connected to the gas side shutoff valve (26). The other end ofthe gas side connecting pipe (17) diverges into two branches one ofwhich is connected to an end of the first indoor circuit (60) on theside of the first indoor heat exchanger (61) and the other of which isconnected to an end of the second indoor circuit (65) on the side of thesecond indoor heat exchanger (66).

[0079] The outdoor unit (11) is provided with an outdoor fan (70). Theoutdoor fan (70) serves to deliver outdoor air to the outdoor heatexchanger (22). Each of the first indoor unit (12) and the second indoorunit (13) is provided with an indoor fan (80). The indoor fans (80)serve to deliver indoor air to the indoor heat exchangers (61, 66).

[0080] The air conditioning system (10) is provided with a temperaturesensor, a pressure sensor, and other sensors. More specifically, theoutdoor unit (11) is provided with an outside air temperature sensor(71) for outside air temperature detection. The outdoor heat exchanger(22) is provided with an outdoor heat exchanger temperature sensor (72)for heat transfer pipe temperature detection. The suction pipe (43) isprovided with a suction pipe temperature sensor (73) for detecting thetemperature of refrigerant which is drawn in the compressors (41, 42),and a low-pressure pressure sensor (74) which detects the pressure ofrefrigerant which is drawn in the compressor (41, 42) and whichconstitutes a temperature detecting means. The discharge pipe (44) isprovided with a discharge pipe temperature sensor (75) for detecting thetemperature of refrigerant discharged from the compressors (41, 42), ahigh-pressure pressure sensor (76) which detects the pressure ofrefrigerant discharged from the compressors (41, 42) and whichconstitutes a temperature detecting means, and a high-pressure pressureswitch (77).

[0081] Each of the indoor units (12, 13) is provided with an inside airtemperature sensor (81) for indoor air temperature detection. Each ofthe indoor heat exchangers (61, 66) is provided with an indoor heatexchanger temperature sensor (82) for heat transfer pipe temperaturedetection. Provided in portions of the indoor circuit (60, 65) in thevicinity of the upper ends of the indoor heat exchangers (61, 66) aregas side temperature sensors (83).

[0082] The controller (90) is configured so as to control the operationof the air conditioning system (10) in response to signals from theabove-described sensors and command signals from a remote controller orthe like. More specifically, the controller (90) performs: the adjustingof the degree of opening of the outdoor expansion valve (24) and indoorexpansion valves (62, 67); the switching of the four-way selector valve(21); and the opening/closing operation of the gas vent solenoid valve(36), oil return solenoid valve (53) and oil-amount averaging solenoidvalve (55).

[0083] The controller (90) is further provided with a capacitycontrolling means (91) and a target value adjusting means (92). And, thetarget value adjusting means (92) includes an air conditioning capacitydeciding means (93) and an air conditioning capacity altering means(94).

[0084] The capacity controlling means (91) controls the air conditioningcapacity of the outdoor unit (11) in such a way that the temperature ofrefrigerant, which is a refrigerant physical quantity, becomes a targetvalue. More specifically, the capacity controlling means (91) isconfigured as follows. During cooling mode operations, the capacitycontrolling means (91) takes a refrigerant evaporating temperature as atarget value and controls the air conditioning capacity of the outdoorunit (11) so that a saturation temperature (evaporating temperature)corresponding to an evaporating pressure detected by the low-pressurepressure sensor (74) becomes a target value. Further, the capacitycontrolling means (91) is configured as follows. During heating modeoperations, the capacity controlling means (91) takes a refrigerantcondensing temperature as a target value and controls the airconditioning capacity of the outdoor unit (11) so that a saturationtemperature (condensing temperature) corresponding to a condensingpressure detected by the high-pressure pressure sensor (76) becomes atarget value.

[0085] The target value adjusting means (92) is configured such that thetarget value of the capacity controlling means (91) is altered. That is,the target value adjusting means (92) is configured so as to predict theload characteristics of a building in which the air conditioning system(10) has been installed, for altering the target value.

[0086] Because of this, the deciding means (93) determines the controlcharacteristics of the target value correspondingly to the airconditioning load characteristics of the building. More specifically,the deciding means (93) is configured so as to determine the controlcharacteristics of the target value of the evaporating temperatureduring cooling mode operations. Also, the deciding means (93) isconfigured so as to determine the control characteristics of the targetvalue of the condensing temperature during heating mode operations.Control characteristic determination by the deciding means (93) may becarried out either manually or by learning.

[0087] Further, the altering means (94) variably alters, according tothe control characteristic determined by the deciding means (93) andbased on the temperature difference between a set temperature of a roomas an air conditioning space and the temperature of outside air which isan outside temperature, the target value. More specifically, thealtering means (94) is configured so as to variably alter the targetvalue of the evaporating temperature during cooling mode operations.Also, the altering means (94) is configured so as to variably alter thetarget value of the condensing temperature during heating modeoperations.

[0088] A basic principle of variably controlling the aforementionedevaporating and condensing temperatures will be described below.

[0089]FIG. 2 shows the cooling load characteristics of buildings inwhich the air conditioning system (10) is installed. That is, eachbuilding has its own inherent load characteristics, and the loadcharacteristics of each building are determined based on the amount ofinternal heat generation and the amount of external heat. Therefore, thecooling load characteristics shown in FIG. 2 show the amounts ofinternal heat generation such as personal computer equipment or thelike. FIG. 2 shows load characteristics (A1-A5) by ratio of the capacityrequired for actual cooling with respect to a cooling capacity (A0, B0)of 100% which is a rated capacity of the air conditioning system (10).

[0090] For example, if the indoor set temperature is 27 degreesCentigrade (which is a standard state) and if the outside airtemperature is also 27 degrees Centigrade, then the inside/outsidetemperature difference is zero degrees Centigrade. In such a condition,if an internal heat generation amount, such as personal computerequipment, does not exist at all, there is no cooling load, and thecooling capacity of the air conditioning system (10) is 0%. Therefore,the operation of the air conditioning system (10) is brought into ahalt.

[0091] Further, if the indoor set temperature is 27 degrees Centigradeand if the outside air temperature is 35 degrees Centigrade, theinside/outside temperature difference is eight degrees Centigrade, thenthe air conditioning system (10) needs a cooling capacity of 100%. Inother words, in addition to the internal heat generation, there exists,for example, penetrating heat from the outside which is an external heatamount. As a result, the air conditioning system (10) is operated at itsmaximum capacity (A0, B0).

[0092] As described above, the cooling capacity of the air conditioningsystem (10) is determined by the internal heat generation based on thecharacteristics of a building and the inside/outside temperaturedifference.

[0093] For example, if, in the above-described state that theinside/outside temperature difference is zero degrees Centigrade, theair conditioning system (10) requires a cooling capacity of 50% (see A1of FIG. 2), then internal heat generation of for example personalcomputer equipment becomes a load. This cooling capacity of 50% isconsumed to deal with such a load. This building is represented by a 50%load characteristic line (A1).

[0094] Each building in which the air conditioning system (10) isinstalled differs in cooling load characteristics from another building.The buildings are represented by the linear load characteristic lines(A1-A5), respectively.

[0095] In FIG. 2, the load characteristic lines (A1-A5) indicated bybroken lines represent the load characteristics of the buildings inthemselves, and the load characteristics (B1-B5) indicated by solidlines, which take account of the safety factor, represent the loadcharacteristics of the buildings which are imposed on the airconditioning system (10). Therefore, the air conditioning system (10)installed is controlled along a solid-line load characteristic line.Further, a cooling capacity of 30% is set as a capacity lower limit.

[0096]FIG. 3 shows control characteristics (C1-C5) of the target valueof the evaporating temperature corresponding to the building coolingload characteristics (B1-B5). In other words, the cooling capacity ofthe air conditioning system (10) is determined correspondingly to thebuilding cooling load characteristics (B1-B5), so that a target value ofthe evaporating temperature for exhibiting such a determined coolingcapacity is determined. For example, a building represented by the 50%load characteristic line (B1) can be represented by the 50% controlcharacteristic line (C1). In this way, the respective buildings can berepresented by the linear target value control characteristic lines(C1-C5) correspondingly to the load characteristic lines (B1-B5).

[0097] For example, for the case of a building of the 50% loadcharacteristic line (C1), the target value of the evaporatingtemperature is 11 degrees Centigrade if the set temperature and theoutside air temperature are the same, and the air conditioning system(10) operates at a cooling capacity of 50%. And, for the case of abuilding of the 50% load characteristic line (B1), the evaporatingtemperature target value is altered, based on the inside/outsidetemperature difference, along the control characteristic line (C1).

[0098] For example, when the set temperature and the outside airtemperature are the same, the outdoor unit (11) controls the capacity ofboth the compressors (41, 42) in order that the evaporating temperaturemay become eleven degrees Centigrade. Further, a target upper limit ofthe evaporating temperature target value is set.

[0099] The same that has been applied to the cooling is applicable tothe heating. FIG. 4 shows the heating load characteristics of buildingsin which the air conditioning system (10) is installed. That is, theheating load characteristics shown in FIG. 4 represent building internalheat generation amounts such as personal computer equipment. And, FIG. 4shows a load characteristic (D1) represented by ratio of the capacityrequired for actual heating to the case where the air conditioningsystem (10) operates at a capacity of 100% heating capacity (D0, E0)which is a rated capacity thereof.

[0100] For example, when the indoor set temperature is seven degreesCentigrade and the outside air temperature is seven degrees Centigrade,the inside/outside temperature difference is zero degrees Centigrade. Insuch a condition, if an internal heat generation amount, such aspersonal computer equipment, does not exist, there is only transmissionof heat to the outside and the heating capacity of the air conditioningsystem (10) is 100%. The air conditioning system (10) will be operatedat its maximum capacity (D0, E0).

[0101] If the indoor set temperature is higher than the outside airtemperature, this produces an inside/outside temperature difference, andinternal heat generation is added to the transmission of heat (which isan external heat amount) to the outside. As a result, the airconditioning system (10) will be operated at a capacity less than themaximum capacity (D0, E0).

[0102] In the way as described above, the heating capacity of the airconditioning system (10), is determined by the internal heat generationbased on the characteristics of a building and the inside/outsidetemperature difference. In other words, each building in which the airconditioning system (10) is installed differs in heating loadcharacteristics from every other building and is represented by thelinear load characteristic line (D1).

[0103] In FIG. 4, the load characteristic line (D1) indicated by abroken line represents the load characteristics of the buildings inthemselves, and the load characteristic line (E1) indicated by a solidline takes account of the safety factor and represents the loadcharacteristics of the buildings which are imposed on the airconditioning system (10). Therefore, the air conditioning system (10)installed is controlled along the solid-line load characteristic line(E1). Further, a heating capacity of 30% is set as a capacity lowerlimit.

[0104]FIG. 5 shows a control characteristic (F1) of the target value ofthe condensing temperature corresponding to the building heating loadcharacteristic(E1). In other words, the heating capacity of the airconditioning system (10) is determined correspondingly to the buildingheating load characteristics (E1), so that a target value of thecondensing temperature for exhibiting such a determined heating capacityis determined. In this way, the respective buildings can be representedby the linear target value control characteristic line (F1)correspondingly to the load characteristic line (E1).

[0105] For example, for the case of a building of the loadcharacteristic line (E1), based on the inside/outside temperaturedifference, the target value of the condensing temperature is alteredalong the control characteristic line (F1) in order that the airconditioning system (10) may exhibit a heating capacity to the loadcharacteristic line (E1). More specifically, the air conditioning system(10) controls the capacity of both the compressors (41, 42) so that thecondensing temperature is along the control characteristic line (F1).Further, a target lower limit of the condensing temperature target valueis set.

[0106] Next, the learning control of the deciding means (93) will bedescribed.

[0107] The deciding means (93) is configured so as to set the controlcharacteristics of the target value by leaning according to the numberof times air conditioning operation is brought to a halt. A halt incooling and heating operation is a so-called “thermo off” state in whichan indoor fan is driven and refrigerant circulation halts. On the otherhand, if the refrigerant circulation is resumed from such a halt state,this is a so-called “thermo on” state in which cooling or the like is inoperation.

[0108]FIG. 6 shows learning control during cooling mode operations. FIG.7 shows learning control during heating mode operations. In FIG. 6, itis sufficient that the cooling capacity of the air conditioning system(10) be altered so as to conform to a building load characteristic line(G). The capacity characteristic line (G) indicated by a solid line isfor example an initial characteristic line set at the time ofinstallation and is a building load factor.

[0109] The deciding means (93) alters, based on the number of times the“thermo off” state occurs during cooling mode operations, a capacitycharacteristic line (H), to determine a target value of the evaporatingtemperature. Like the building load characteristic line (G), thecapacity characteristic line (H) is linear. Therefore, if the capacitycharacteristics of two points differing in the inside/outsidetemperature difference are determined, this determines the capacitycharacteristic line (H). The capacity characteristic line (H) is a ratiowith respect to a capacity of 100% and is a capacity target ratio.

[0110] Further, the same is applicable to the heating. In FIG. 7, it issufficient that the heating capacity of the air conditioning system (10)be altered so as to conform to a building load characteristic line (J).The capacity characteristic line (J) indicated by a solid line is forexample an initial characteristic line set at the time of installationand is a building load factor.

[0111] The deciding means (93) alters, based on the number of times the“thermo off” state occurs during heating mode operations, a capacitycharacteristic line (L), to determine a target value of the condensingtemperature. Like the building load characteristic line (J), thecapacity characteristic line (L) is linear. Therefore, if the capacitycharacteristics of two points differing in the inside/outsidetemperature difference are determined, this determines the capacitycharacteristic line (L). The capacity characteristic line (L) is a ratiowith respect to a capacity of 100% and is a capacity target rate.

[0112] The principle of learning for example during cooling modeoperations will be described. As shown in FIG. 8, a region M where thedifference between inside and outside temperature increases by more thanfive degrees Centigrade and thereafter decreases by less than threedegrees Centigrade, and a region N where the inside/outside temperaturedifference decreases by less than three degrees Centigrade andthereafter increases by more than five degrees Centigrade, are set.

[0113] The number of times the “thermo off” state occurs in the region Mis counted, and if the “thermo off” state often occurs, a capacity value(K2) at a specified value (eight degrees Centigrade) of the presetinside/outside temperature difference is decreased. On the other hand,if no “thermo off” state occurs, then the capacity value (K2) isincreased.

[0114] Further, the number of times the “thermo off” state occurs in theregion N is counted, and if the “thermo off” state often occurs, acapacity value (K1) at a specified value (zero degrees Centigrade) ofthe preset inside/outside temperature difference is decreased. On theother hand, if no “thermo off” state occurs, then the capacity value(K1) is increased.

[0115] When these two points (K1, K2) of the regions M and N aredetermined, the capacity characteristic line (G) can be determined. Thenumber of times the “thermo off” state occurs is a count for one hourduring heating mode operations, and ideally the smallest possible“thermo off” count is preferable.

[0116] Operation

[0117] Hereinafter, the operation of the air conditioning system (10)will be described.

[0118] In the air conditioning system (10), refrigerant circulates inthe refrigerant circuit (15) while undergoing a change of phase, andswitching between a cooling mode operation and a heating mode operationis carried out.

[0119] Cooling Mode Operation

[0120] During cooling mode operations, cooling operation, in which eachindoor heat exchanger (61, 66) acts as an evaporator, is carried out. Insuch cooling operation, the four-way selector valve (21) is placed inthe state indicated by a solid line of FIG. 1. Further, the outdoorexpansion valve (24) is fully opened, and the degree of opening of thefirst indoor expansion valve (62) and that of the second indoorexpansion valve (67) are adjusted to respective specified values. Thegas vent solenoid valve (36) remains in the closed state, and the oilreturn solenoid valve (53) and the oil amount averaging solenoid valve(55) are adequately opened and closed.

[0121] When the compressors (41, 42) of the compressor unit (40) are inoperation, refrigerant compressed in each of these compressors (41, 42)is discharged to the discharge pipe (44). The refrigerant, after passingthrough the four-way selector valve (21), flows in the outdoor heatexchanger (22). In the outdoor heat exchanger (22), the refrigerantgives off the heat to outdoor air and then condenses. The refrigerantthus condensed flows through the first branch pipe (30 a) of the inflowpipe (30), passes through the first inflow check valve (31), and flowsinto the receiver (23). Thereafter, the refrigerant leaves the receiver(23), flows through the outflow pipe (33), passes through the outflowcheck valve (34), and flows into the liquid side connecting pipe (16).

[0122] After having flowed through the liquid side connecting pipe (16),the refrigerant diverges into two flows one of which enters into thefirst indoor circuit (60) and the other of which enters into the secondindoor circuit (65). In the indoor circuit (60, 65), the refrigerant isdepressurized in the indoor expansion valve (62, 67) and thereafterflows into the indoor heat exchanger (61, 66). In the indoor heatexchanger (61, 66), the refrigerant absorbs heat and then evaporates. Inother words, in the indoor heat exchanger (61, 66), indoor air iscooled.

[0123] The refrigerants, which have been evaporated in the indoor heatexchangers (61, 66), flow through the gas side connecting pipe (17),merge, and flow into the outdoor circuit (20). Thereafter, therefrigerant passes through the four-way selector valve (21) and thesuction pipe (43) and is drawn into the compressors (41, 42) of thecompressor unit (40). These compressors (41, 42) each compress therefrigerant drawn thereinto and discharge it again. In the refrigerantcircuit (15), such a circulation of refrigerant is repeatedly carriedout.

[0124] Heating Mode Operation

[0125] During heating mode operations, heating operation, in which eachindoor heat exchanger (61, 66) acts as a condenser, is carried out. Insuch heating operation, the four-way selector valve (21) is placed inthe state indicated by a broken line of FIG. 1. Further, the outdoorexpansion valve (24), the first indoor expansion valve (62), and thesecond indoor expansion valve (67) are adjusted to respective specifiedopening degrees. The oil return solenoid valve (53) and the oil amountaveraging solenoid valve (55) are adequately opened and closed. Further,the gas vent solenoid valve (36) is held in the opened state all thetime during the heating operation.

[0126] When the compressors (41, 42) of the compressor unit (40) are inoperation, refrigerant compressed in each of these compressors (41, 42)is discharged to the discharge pipe (44). The refrigerant, after passingthrough the four-way selector valve (21), flows through the gas sideconnecting pipe (17) and is distributed to each indoor circuit (60, 65).

[0127] The refrigerants, which have flowed into the indoor circuits (60,65), give off the heat to indoor air and then condense in the indoorheat exchangers (61, 65). In each indoor heat exchanger (61, 65), indoorair is heated by heat given off from the refrigerant. The refrigerantcondensed is depressurized in each indoor expansion valve (62, 67),passes through the liquid side connecting pipe (16), and flows into theoutdoor circuit (20).

[0128] The refrigerant, which has flowed into the outdoor circuit (20),flows through the second branch pipe (30 b) of the inflow pipe (30),passes through the second inflow check valve (32), and flows into thereceiver (23). Thereafter, the refrigerant leaves the receiver (23),flows through the outflow pipe (33), passes through the outdoorexpansion valve (24), and flows in the outdoor heat exchanger (22). Inthe outdoor heat exchanger (22), the refrigerant absorbs heat fromoutdoor air and then evaporates. The evaporated refrigerant passesthrough the four-way selector valve (21), passes through the suctionpipe (43), and is drawn into the compressors (41, 42) of the compressorunit (40). These compressors (41, 42) each compress the refrigerantdrawn thereinto and discharge it again. In the refrigerant circuit (15),such a circulation of refrigerant is repeatedly carried out.

[0129] Capacity Control

[0130] Referring to FIG. 9, the capacity control of the outdoor unit(11) will be described. FIG. 9 shows a cooling mode operation.

[0131] In the first place, in STEP ST1 it is decided whether to learnthe load characteristics of a building in which the air conditioningsystem (10) has been installed, at the time of installation of the airconditioning system (10) or at the time when the air conditioning system(10) is brought into a halt. Such a decision on whether to learn theload characteristics of the building is made, for example by performinga setting on a control part of each indoor unit (12, 13).

[0132] If the building load characteristics are not to be learned, theprocedure proceeds to STEP ST2. In STEP ST2, an internal heat generationload factor (K1) of the building is set. This internal heat generationload factor (K1) is equivalent to the load characteristics shown in FIG.2 and is a load characteristic when the inside/outside temperaturedifference is zero degrees Centigrade.

[0133] Next, shifting to the control during cooling mode operations, atarget capacity ratio (Q) is calculated in STEP ST3. This targetcapacity ratio (Q) is equivalent to the capacity characteristics shownin FIG. 4. More specifically, based on the following equation (1), thetarget capacity ratio (Q) is calculated from the temperature differencebetween an outside air temperature (To) and a set temperature (Ti) ofthe lower in set temperature of the indoor units (12, 13).

Q={(1−K 1)/8}×(To−TiΔT)+K 1   (1)

[0134] Note that ΔT in Equation (1) is a value corresponding to a safetyfactor. Further, “8” in Equation (1) is an inside/outside temperaturedifference in a standard condition. Further, the target capacity ratio(Q) has a value not more than 1.0 nor less than 0.3 (0.3≦Q≦1.0). Inother words, the target capacity ratio (Q) is so limited as to fall inthe range in which efficient operations can be carried out.

[0135] Next, the procedure proceeds to STEP ST4. In STEP ST4, anevaporating temperature target value (Tes) is determined based on thetarget capacity ratio (Q) and the set temperature (Ti).

Tes=(Ti−8)−(ti−8−Teo)×Q   (2)

[0136] Note that the target value (Tes) in Equation (2) is a value notless than zero and is a temperature at which the indoor units (12, 13)will not undergo freezing. Further, “Teo” is an evaporating temperatureduring rated operation.

[0137] Thereafter, the procedure proceeds to STEP ST5 in which theoutdoor unit (11) controls the capacity of the compressors (41, 42) inorder that the refrigerant evaporating temperature (Te) may become thetarget value (Tes).

[0138] On the other hand, if it is decided in STEP ST1 that the loadcharacteristics of the building are to be learned, then the procedureproceeds to STEP ST6. In this STEP ST2, initial values for the buildinginternal heat generation load factor (K1) and the building maximum loadfactor (K2) are set. This maximum load factor (K2) is equivalent to theload characteristics shown in FIG. 2 and is a load characteristic whenthe inside/outside temperature difference is eight degrees Centigrade.

[0139] Subsequently, shifting to the control during cooling modeoperations, the target capacity ratio (Q) is calculated in STEP ST7.More specifically, based on the following equation (3), the targetcapacity ratio (Q) is calculated from the temperature difference betweenthe outside air temperature (To) and the set temperature (Ti) of thelower in set temperature of the indoor units (12, 13).

Q={(K 2−K 1)/8}×(To−Ti)+K 1   (3)

[0140] Note that “8” in Equation (3) is an inside/outside temperaturedifference in a standard condition. Further, the target capacity ratio(Q) has a value not more than 1.0 nor less than 0.3 (0.3≦Q≦1.0), as inSTEP ST3.

[0141] Next, the procedure proceeds to STEP ST4. In STEP ST4, based onthe target capacity ratio (Q) and the set temperature (Ti), the targetvalue (Tes) of the evaporating temperature (Te) is determined fromEquation (2) in the same way as described above.

[0142] Thereafter, the procedure proceeds to STEP ST5 in which theoutdoor unit (11) controls the capacity of the compressors (41, 42) inorder that the refrigerant evaporating temperature (Te) may become thetarget value (Tes).

[0143] On the other hand, also during heating mode operations, thetarget capacity ratio (Q) is calculated, as in the cooling modeoperations, and a target value (Tcs) of the condensing temperature isdetermined. Thereafter, the outdoor unit (11) controls the capacity ofthe compressors (41, 42) in order that the refrigerant condensingtemperature (Tc) may become the target value (Tcs).

[0144] Conventionally, both the target value (Tes) of the evaporatingtemperature (Te) and the target value (Tcs) of the condensingtemperature are fixed. On the other hand, as shown in FIGS. 3 and 5, theevaporating temperature (Te) increases from the control characteristicline (C0, F0) and the condensing temperature (Tc) decreases therefrom.

[0145] Effects of the Embodiment

[0146] As described above, in accordance with the present embodiment,the air conditioning capacity of the outdoor unit (11) is controlled byaltering, based on a building air conditioning load, a refrigeranttemperature target value. As a result of such arrangement, it ispossible to provide an operation corresponding to the building airconditioning load.

[0147] To sum up, when it is sufficient for each indoor unit (12, 13) tooperate at a small air conditioning capacity, it is possible to causethe outdoor unit (11) to operate also at a small air conditioningcapacity.

[0148] As a result of the above, each indoor unit (12, 13) is preventedfrom undergoing an excess of capacity, for example in an intermediateperiod. Because of this, it is possible to reduce the frequency at eachindoor unit (12, 13) repeatedly undergoes the “Thermo off” state and the“thermo on” state. And, it is possible to reduced the variation inindoor temperature, and it is also possible to stabilize the capacity ofthe compressors (41, 42).

[0149] Furthermore, the frequency at which each compressor (41, 42) isrepeatedly driven and shut down can be reduced, as a result of whichstress which is produced at the time of driving and stopping eachcompressor (41, 42) can be reduced thereby making it possible to improvethe durability of the compressors (41, 42).

[0150] Additionally, since it is possible to suppress an excess of airconditioning capacity, this provides improvement in operating efficiencythereby making it possible to provide improvements not only in COP(Coefficient Of Performance) but also in economy.

[0151] Further, a target value can be altered based on the differencebetween a set temperature and an outside air temperature, thereby makingit possible to provide an increased air conditioning capacity forexample at the beginning of an operation. For example, if the indoortemperature is higher than a set temperature in a cooling modeoperation, or if the indoor temperature is lower than a set temperaturein a heating mode operation, this increases the difference between theevaporating temperature of refrigerant or the condensing temperature ofrefrigerant and the temperature of indoor suction air. Therefore it ispossible to provide an increased air conditioning capacity. As a result,it is possible to provide improved comfortability.

[0152] Further, even when there occurs sudden variation in load, the airconditioning capacity can be increased by making changes in settemperature. This makes it possible to improve comfortability.

[0153] Furthermore, when performing air conditioning by introducingoutdoor air, the air conditioning capacity varies based on theinside/outside temperature difference, thereby further improvingcomfortability. For example, the capacity of air conditioning requiredto meet a set blowout temperature is determined by the differencebetween the temperature of suction air and the set temperature ofblowout air. In accordance with the present invention, the heat sourceunit (11) is able to control required minimum capacity, thereby makingit possible to improve COP and extend the range of controllableoperation.

[0154] Further, if it is arranged such that the control characteristicsof the target value can be manually set, this provides air conditioningcapacity to the comfortability of a resident. For example, for the caseof a resident who is interested in energy savings, energy-savingoperations can be carried out. This certainly provides improvements ineconomy as well as in comfortability.

[0155] Furthermore, if it is arranged such that the target value controlcharacteristics can be learned, then air conditioning capacitycorresponding to an air conditioning load of the building can be setautomatically. This provides further improvements in economy as well asin comfortability.

[0156] Other Embodiments

[0157] Although in the above-described embodiment the target valuecontrol characteristics are either manually set or learned, the network(9 b) which is an external setting means may be used. More specifically,as indicated by a long dashed short dashed line of FIG. 1, anarrangement may be made in which a controller is connected, through thecommunication line (9 a), to the network (9 b) and the controlcharacteristics of a target value are set via the network (9 b).

[0158] The target value adjusting means (92) of the above-describedembodiment includes the deciding means (93) and the altering means (94).To sum up, it is sufficient for the present invention that target valuescan be controlled variably. Accordingly, it is sufficient that thetarget value adjusting means (92) is configured so as to variablycontrol a target value correspondingly to the air conditioning loadcharacteristics of a building. Further, the target value adjusting means(92) may be configured so as to variably control, according to thecontrol characteristics of a target value and based on the differencebetween the set temperature of an air conditioning space and externaltemperature, the target value.

[0159] Furthermore, for the case of the capacity controlling means (91)and the target value adjusting means (92) of the above-describedembodiment, as a target value which is a refrigerant physical amount,evaporating temperature and condensing temperature are used. However,the target value may be an evaporating pressure during a cooling modeoperation and a condensing pressure during a heating mode operationdetected by the low-pressure pressure sensor (74) and by thehigh-pressure pressure sensor (76).

[0160] Further, these temperature detecting means may be the suctionpipe temperature sensor (73) and the discharge pipe temperature sensor(75).

[0161] Finally, the air conditioning system (10) may be an airconditioner capable of providing only cooling or an air conditionercapable of providing only heating and the number of compressors may beone.

INDUSTRIAL APPLICABILITY

[0162] As described above, the air conditioning system of the presentinvention is useful for building air conditioning or the like and isparticularly suitable when provided with a plurality of indoor units.

Wheat is claimed is:
 1. An air conditioning system for providing air conditioning, said air conditioning system comprising a refrigerant circuit (15) formed by connection of a heat source unit (11) and a plurality of utilization units (12, 13, . . . ), wherein the air conditioning capacity of said heat source unit (11) is controlled such that a physical quantity of refrigerant circulating through said refrigerant circuit (15) becomes a target value, and wherein said target value is altered and set.
 2. An air conditioning system for providing air conditioning comprising a refrigerant circuit (15) formed by connection of a heat source unit (11) and a plurality of utilization units (12, 13, . . . ), said air conditioning system further comprising: capacity controlling means (91) for controlling the air conditioning capacity of said heat source unit (11) so that a physical quantity of refrigerant becomes a target value, and target value adjusting means (92) for altering said target value of said capacity controlling means (91).
 3. The air conditioning system of claim 2, wherein said target value adjusting means (92) is configured so as to variably control said target value correspondingly to the air conditioning load characteristics of a building.
 4. The air conditioning system of claim 2, wherein said target value adjusting means (92) is configured so as to variably control, according to the control characteristics of said target value and based on the temperature difference between a set temperature of an air conditioning space and an outside temperature, said target value.
 5. The air conditioning system of claim 2, wherein said target value adjusting means (92) includes deciding means (93) for determining the control characteristics of said target value correspondingly to the air conditioning load characteristics of a building, and altering means (94) for variably controlling, according to said target value control characteristics determined by said deciding means (93) and based on the temperature difference between a set temperature of an air conditioning space and an outside temperature, said target value.
 6. The air conditioning system of any one of claims 1-5, wherein during cooling mode operations said refrigerant physical quantity is an evaporating pressure.
 7. The air conditioning system of any one of claims 1-5, wherein during cooling mode operations said refrigerant physical quantity is an evaporating temperature.
 8. The air conditioning system of any one of claims 1-5, wherein during heating mode operations said refrigerant physical quantity is a condensing pressure.
 9. The air conditioning system of any one of claims 1-5, wherein during heating mode operations said refrigerant physical quantity is a condensing temperature.
 10. The air conditioning system of any one of claims 1-5, wherein the air conditioning capacity of said heat source unit (11) is controlled by controlling the capacity of each compressor (41, 42) of said heat source unit (11).
 11. The air conditioning system of either claim 3 or claim 5, wherein said building load characteristics are determined based on the amount of internal heat generation of said building and the amount of external heat.
 12. The air conditioning system of claim 5, wherein: temperature detecting means (74) for the detection of refrigerant evaporating temperatures during cooling mode operations is provided, said capacity controlling means (91), which takes as a refrigerant evaporating temperature a target value during cooling mode operations, is configured to control the air conditioning capacity of said heat source unit (11) so that an evaporating temperature that said temperature detecting means (74) detects becomes said target value, said deciding means (93) of said target value adjusting means (92) is configured so as to determine the control characteristics of said target value of said evaporating temperature, and said altering means (94) of said target value adjusting means (92) is configured so as to variably control said target value of said evaporating temperature.
 13. The air conditioning system of claim 5, wherein: temperature detecting means (76) for the detection of refrigerant condensing temperatures during heating mode operations is provided, said capacity controlling means (91), which takes as a refrigerant condensing temperature a target value during heating mode operations, is configured to control the air conditioning capacity of said heat source unit (11) so that a condensing temperature that said temperature detecting means (76) detects becomes said target value, said deciding means (93) of said target value adjusting means (92) is configured so as to determine the control characteristics of said target value of said condensing temperature, and said altering means (94) of said target value adjusting means (92) is configured so as to variably control said target value of said condensing temperature.
 14. The air conditioning system of any one of claims 4, 5, 12, and 13, wherein said target value adjusting means (92) is configured such that said target value control characteristics are set manually.
 15. The air conditioning system of any one of claims 4, 5, 12, and 13, wherein said target value adjusting means (92) is configured such that said target value control characteristics are set based on an input signal fed from external setting means (9 b) via a communication line (9 a).
 16. The air conditioning system of any one of claims 4, 5, 12, and 13, wherein said target value adjusting means (92) is configured such said target value control characteristics are automatically set by learning according to the state of an operation during air conditioning.
 17. The air conditioning system of claim 16, wherein said deciding means (93) of said target value adjusting means (92) is configured such that said target value control characteristics are set by learning according to the number of times air conditioning operation halts. 